As an extension of a study (Virology, 112, 365-369, 1981) documenting the preferential expression of p26 antigen from Macaca arctoides type C virus (MAC-1) in Macaca mulatta trophoblast, cocultivation of isolated trophoblasts from rhesus placentas with three indicator cell lines (A549, FEC, and CF2Th) were carried out which led to rapid isolation (3 to 4 weeks) in FEC of type C rhesus retrovirus in 4 of 10 cases. Melting curves of DNA-DNA hybridization indicated a 2 degree difference (83oC vs. 81oC) between these M. mulatta isolates and the single M. arctoides isolate. Previous isolates from Macaca were obtained in single, long term experiments (over 7 months). Consequently, primary trophoblasts represent a useful differentiated cell source for isolation of infectious retrovirus from a "low producer" primate species. Growth factors of apparent molecular weights of 6,000, 10,000, 20,000, and one in excess of 30,000 can be isolated from acid ethanol/extracts of human term placentas. Each size class of polypeptide has the defining properties of transforming growth factors (TGFs). By homologous radioimmunoassay, neither the 6,000 nor the 10,000 dalton polypeptide is related to human epidermal growth factor. The presence of these TGFs in ample concentrations indicates the usefulness of this tissue source for the study of human TGFs.